1. Field of the Invention
The present invention relates to loaders and bonding apparatus for fabricating a liquid crystal display device, and more particularly, to a loader for fabricating a liquid crystal display device, in which a substrate can be inverted without using a separate inverting device, and sagging of a large sized substrate is prevented, to enable easy loading the substrate onto a bonding apparatus, a bonding apparatus which enables easy separation of bonded substrates from an upper stage when the upper stage moves up after bonding the substrates, and a method for loading a substrate using the same.
2. Discussion of the Related Art
Keeping pace with development of an information oriented society, demands for display devices increase gradually in various forms. Recently, to meet the demands, various flat display devices, such as LCD (Liquid Crystal Display Device), PDP (Plasma Display Panel), ELD (Electro Luminescent Display), VFD (Vacuum Fluorescent Display), have been studied, and some of which are used as display devices in various apparatuses.
Of the various display devices, currently the LCD is used mostly for mobile display devices because of advantages such as good picture quality, light weight, thin, and low power consumption, while replacing the CRT (Cathode Ray Tube). Besides the mobile display devices, such as monitors for notebook computers, the LCD is being developed for use as a monitor for televisions for receiving and displaying a broadcasting signal and for use as a monitor for computers.
Despite various technical developments, for the LCD to serve as display devices in various fields, efforts for enhancing the picture quality are contradictory to above advantages in many aspects. Therefore, for using the LCD in various fields as general display devices, a key to development of the LCD lies on the extent of realization of a high quality picture, such as high definition, high luminance, and large sized picture, while the features of light weight, thin, and low power consumption are maintained.
Such an LCD is provided with a liquid crystal panel for displaying a picture, and a driving unit for applying a driving signal to the liquid crystal panel. The liquid crystal display panel is provided with upper and lower substrates bonded together, with a space between the substrates, and a liquid crystal layer between the upper, and the lower substrates.
Formed on the first glass substrate (a TFT array substrate) are a plurality of gate lines arranged at regular intervals in one direction, a plurality of data lines arranged at regular intervals perpendicular to the gate lines, a plurality of pixel electrodes on every pixel region defined at every cross of the gate lines and the data lines in a form of matrix, and a plurality of thin film transistors (TFT) to be switched in response to a signal on the gate line for transmission of a signal on the data line to each pixel electrode.
Formed on the upper substrate (a color filter substrate) are a black matrix layer for shielding a light incident on parts excluding the pixel regions, R, G, B color filter layers for expressing colors, and a common electrode for displaying a picture.
The first, and second substrates are bonded with sealant with a space between the substrates provided by means of spacers.
For bonding the two substrates, one of the two substrates is inverted to face each other, and the two substrates are loaded on the bonding apparatus for bonding.
There are different methods for forming the liquid crystal layer between the two substrates: a liquid crystal injecting method and a liquid crystal dispensing method.
In the liquid crystal injecting method, a sealant pattern is formed to have a liquid crystal injection hole before bonding the two substrates together. The bonded two substrates are cut into unit liquid crystal display panels. Thus, a liquid crystal injection hole in each of unit liquid crystal display panel exposed and the unit panel is dipped into liquid crystal, while maintaining a vacuum between the two substrates, to inject the liquid crystal between the two substrates by capillary tube phenomenon. Once the liquid crystal is injected thus, the liquid crystal injection hole is sealed with a sealant.
However, such a liquid crystal injection type LCD fabricating method has a poor productivity because of the cutting into unit liquid crystal display panels, and dipping of the liquid crystal injection hole in each of unit liquid crystal display panel into liquid crystal liquid while maintaining a vacuum between the two substrates, all of which require a lot of time. Also, for fabrication of a large sized liquid crystal display device, imperfect injection of the liquid crystal into the panel causes defects.
Therefore, the applicant has filed a U.S. patent application Ser. No. 10/126,963 disclosing a bonding apparatus for bonding two substrates after dispensing an appropriate amount of liquid crystal on each liquid crystal display panel regions before the bonding of the two substrates.
FIG. 1 schematically illustrates a bonding apparatus (U.S. patent application Ser. No. 10/126,963) filed by the applicant; FIGS. 2A and 2C schematically illustrate sections of the loader unit and the upper stage in FIG. 1; and FIGS. 3A-3C illustrates the steps of the bonding method in FIG. 1.
Referring to FIG. 1, the LCD bonding apparatus is provided with a vacuum chamber 110, a stage unit, a stage moving device, a vacuum unit, a vent device, and a loader unit 30.
The vacuum chamber 110 has an inside space which becomes a vacuum state or an atmospheric pressure state selectively, for carrying out bonding by application of a pressure between substrates, and bonding by using a pressure difference between the substrates in succession, and an opening 111 in a peripheral surface thereof for putting in/taking out the substrates.
The vacuum chamber 110 has an air discharge pipe 112 connected to one side of the peripheral surface for receiving air suction force from the vacuum device and discharging air from the inside space, and a vent pipe 113 connected to one side of the peripheral surface for receiving air or other gas (N2) from an outside of the space, and maintaining the space in an atmospheric state, thereby enabling the inside space to be in a vacuum state or to release the vacuum state, selectively.
The air discharge pipe 112 and the vent pipe 113 have electronically controlled shut off valves 112a and 113a provided thereon, respectively, for selective shut off of the pipes.
The stage unit has an upper stage 121 and a lower stage 122 mounted in an upper space and a lower space of the vacuum chamber 110 to face each other, for holding respective substrates 10 and 20 put into the vacuum chamber 110 by the loader unit 30 at required working positions.
The upper, and lower stages 121 and 122 are respectively provided with at least one Electro Static Chuck (ESC) 121a, and 122a mounted in a recess thereof for providing static force thereto for holding the substrate and at least one vacuum hole 121b for receiving vacuum force to hold the substrate with the vacuum.
Each of the electro static chucks 121a and 122a has a plurality of flat electrode pairs for applying DC currents of opposite polarity thereto for making an electro static attachment.
The vacuum holes 121b in the upper stage 121 formed around each of the electro static chucks 121a in an underside surface of the upper stage 121 are in communication through one or a plurality of pipe lines 121c for receiving the vacuum force from a vacuum pump 123 connected to the upper stage 121.
The lower stage 122 has at least one electro static chuck 122a mounted in an upper surface thereof for providing static force to hold the substrate, and at least one vacuum hole (not shown) in the upper surface for receiving the vacuum force to adsorb and hold the substrate.
The stage moving device has a moving shaft 131 for moving the upper stage 121 in up/down direction selectively, a rotating shaft 132 for rotating the lower stage 122 in left/right direction, and driving motors 133 and 134 respectively shaft coupled to the stages 121 and 122 at an inside or outside of the vacuum chamber 110 for driving respective shaft, selectively.
The vacuum device provides the vacuum force to the vacuum chamber 110 so that the vacuum chamber 110 is in a vacuum state selectively, and has a vacuum pump for absorbing air to form a vacuum. A space in the vacuum pump 200 is in communication with the air discharge pipe 112 in the vacuum chamber 110.
The loader unit 30, a separate device from the vacuum chamber 110 and various units in the vacuum chamber 110, is installed on an outside of the vacuum chamber 110, for receiving the first substrate 10 having liquid crystal dispensed thereon and the second substrate 20 having the sealant coated thereon and for putting into or taking out of the vacuum chamber 110 of the bonding apparatus.
The loader unit is provided with a first arm 31 for carrying the first substrate 10 having the liquid crystal dispensed thereon, and a second arm 32 for carrying the second substrate 20 having the sealant coated thereon. As illustrated in FIGS. 2A-2C, each of the first and second arms 31 and 32 has at least two robot fingers 32a and 32b for placing the first or second substrate 10 or 20 thereon. Even though more robot fingers are better for stable loading of the substrate on the vacuum chamber, the number of the robot fingers are limited because it is required that the robot finger is only in contact with a non-display region of the substrate, which is in a state adsorbed to the upper stage in an inverted state.
Taking into account that the first substrate 10 to be placed on the first arm 31 is in a state the liquid crystal are dispensed thereon and that the second substrate 20 to be placed on the second arm 32 has a side having the sealant coated thereon faced downward, the first arm 31 is positioned over the second arm 32 in a standby state before the substrate is carried into the inside of the vacuum chamber 110 for preventing various foreign matter formed as the second arm 32 moves from flying down onto the liquid crystal on the first substrate 10 placed on the first arm 31, which might occur if the second arm 32 is positioned over the first arm 31 in advance.
Moreover, an aligning device 60 is provided for verifying alignment of the substrates 10 and 20 carried into the vacuum chamber 110 by the loader unit and loaded on respective stages 121 and 122.
A method for fabricating a liquid crystal display device by using the bonding apparatus will be described.
The first substrate 10 having the thin film transistor array formed thereon, and the liquid crystal dispensed thereon, and the second substrate 20 having the color filter array formed thereon, and the sealant coated thereon, are provided.
Then, after the second substrate 20 is inverted such that a side having the sealant coated thereon faces downward, the loader unit 30 causes the first substrate 10 having the liquid crystal dispensed thereon to standby on the first arm 31 and the second substrate 20 having the sealant coated thereon to standby on the second arm 32.
In this state, if the opening 111 in the vacuum chamber 110 is opened, as illustrated with a dash line in FIG. 1, the loader unit 30 controls the second arm 32 so that the second arm 32 carries the second substrate 20 having the sealant coated thereon onto the upper stage 121 in the upper space of the vacuum chamber 110 through the opening 111, controls the upper stage 121 to adsorb the second substrate 20 by vacuum, and, thereafter, controls the first arm 31 so that the first arm 31 carries the first substrate 10 having the liquid crystal dispensed thereon onto the lower stage 122 in the lower space of the vacuum chamber 110, and controls the lower stage 122 to adsorb the first substrate 10 by vacuum.
A method for adsorbing the second substrate 20 to the upper stage 121 will be described in more detail.
Referring to FIG. 2A, since the second substrate 20 is in an inverted state in which the side of the second substrate 20 having the sealant coated thereon faces downward, the second arm is positioned to the second substrate 20, such that the non-display regions of the second substrate 10 are in contact with the robot fingers 32a and 32b, and the second arm 32 is positioned under the upper stage 121 in the vacuum chamber 110.
Then, the upper stage 121 moves down until the upper stage 121 is in contact with the second substrate 20 on the second arm 32, and as illustrated in FIG. 2C, the upper stage adsorbs the second substrate 20 by vacuum and moves up.
In above process, if there are bonded substrates on the lower stage because a bonding process occurred right before, by unloading the bonded substrate present on the lower stage after the second arm 32 that carried in the second substrate 20 makes the second substrate adsorbed to the upper stage, loading and unloading can be carried out at the same time, to shorten a process time period.
Referring to FIG. 3A, upon finishing loading of the substrates 10, and 20 on the upper stage 121 and the lower stage 122, respectively, by above process, the arms 31 and 32 of the loader unit 30 move away from the vacuum chamber 110, and a door (not shown) on the opening 111 of the vacuum chamber 110 closes the opening 111 to enclose the inside space of the vacuum chamber 110.
Thereafter, the vacuum pump 200 operates to generate a vacuum, while the shut off valve 112a on the air discharge pipe 112 of the vacuum chamber 110 is left open, to make the vacuum chamber in a vacuum state.
Thus, when the vacuum chamber 110 is in a vacuum state by a time period of operation of the vacuum pump 200, operation of the vacuum pump 200 stops, and the shut off valve 112a on the air discharge pipe 112 is closed, to close the air discharge pipe 112.
Once the vacuum chamber 110 is in a vacuum state, the upper stage 121 and the lower stage 122 provide power to the electro static chucks 121a, and 122a, to absorb the substrate 10 and 20, respectively.
Under this state, referring to FIG. 3B, the stage moving device puts the driving motor 133 into operation, to move down the upper stage 121 until the upper stage comes close to the lower stage 122, and then, the aligning device 60 verifies alignment of the substrates 10 and 20, respectively, attached to the stages 121 and 122 and provides control signals to the moving shaft 131 and the rotation shaft 133 coupled to the stages 121 and 122, respectively, for alignment of the substrates.
Then, the stage moving device keeps moving in response to driving signal provided thereto continuously, to press down the second substrate 20 attached to the upper stage 121 to the first substrate 10 attached to the lower stage 122 until a primary bonding of the substrates is made.
The primary bonding is not the end of a complete bonding process by pressing through moving of the stages 121 and 122, but bonding enough to prevent infiltration of air between the substrates when the vacuum chamber is turned into an atmospheric pressure state.
Therefore, upon completion of the primary bonding process, the static adsorption force of the upper stage 121 is removed, and the upper stage 121 is separated from the bonded substrates 10 and 20. In this instance, referring to FIG. 3C, it is possible that the bonded substrates 10 and 20 are lifted following the upper stage 121 that is moving upward.
As the shut off valve 113a having closed the vent pipe 113 is operated, the vent pipe 113 is opened, to turn the vacuum chamber 110 into an atmospheric pressure state, to cause a pressure difference between inside and outside of the bonded substrates inside of the vacuum chamber 110, to further press down and bond the substrates, again.
According to this, the bonding between the substrates becomes more perfect. When such a bonding process is finished, the door (not shown) on the vacuum chamber 110 is opened to open the opening 111.
Thereafter, the loader unit 30 unloads the bonded substrates, and above series of steps are repeated to bond successive substrates.
However, the method for loading the substrate, and the method for bonding the substrate in the related art bonding apparatus have the following problems.
First, though the more a number of the robot fingers, the more stable loading of the substrate on the vacuum chamber, the number of the robot fingers are limited because it is required that the robot finger is only in contact with a non-display region of the substrate that is in a state adsorbed to the upper stage in an inverted state.
Second, as illustrated in FIGS. 2A-2C, since the loader unit supports the inverted substrate at edges thereof during loading the substrate in the vacuum chamber, the substrates sags down the more as the size of the substrate becomes the greater, to cause difficulty in adsorbing the substrate to the stage.
Third, since the loader unit is not provided with means for adsorbing the substrate and the arm is not rotatable, requiring a separate inverting device for inverting the substrate that is to be adsorbed to the upper stage before loading the substrate on the bonding apparatus, the cost for a fabrication processing line increases.
Fourth, as illustrated in FIG. 3C, upon completion of the primary bonding process, the static adsorption force of the upper stage is removed, and the upper stage is separated from the bonded substrates when it is possible that the bonded substrates are lifted following the upper stage that is moving upward, to separate the first and second substrates, or to cause infiltration of air between the two substrates, resulting in defect of the bonding.